The present invention relates to polyamide moulding compounds having improved heat-ageing resistance and to moulded articles produced herefrom.
Thermoplastic polyamides are frequently used in the form of glass fibre-reinforced moulding compounds as construction materials for components which are subjected to increased temperatures during their lifespan, the result being thermooxidative damage. By the addition of known heat stabilisers, the occurrence of thermooxidative damage can in fact be delayed but not permanently prevented, which is expressed for example in a decrease in the mechanical characteristic values. Improvement in the heat-ageing resistance of polyamides is extremely desirable since consequently longer lifespans for thermally loaded components can be achieved or the failure risk thereof can be reduced. Alternatively, improved heat-ageing resistance can also enable the use of the components at higher temperatures.
Heat-ageing resistance is still not adequate in the known polyamide moulding compounds, in particular over fairly long thermal loading time periods and at temperatures above 200° C.
Various approaches for improving the heat-ageing resistance are known from the state of the art.
Thus EP 2 535 365 A1 describes a polyamide moulding compound based on partially crystalline, partially aromatic polyamides to which, as heat stabiliser, copper compounds, stabilisers based on secondary aromatic amines or sterically hindered phenols or phosphites or phosphonites are added.
Polyamides which are stabilised against the influences of light and heat are known from GB 904,972. As stabilisers, combinations of hypophosphorous acid and/or hypophosphates in combination with cerium- or titanium salts are described here.
From EP 1 832 624 A1, the use of radical interceptors for stabilising organic polymers against photochemical, thermal, physical or chemically induced degradation is known, cerium dioxide being used here as radical interceptor.